1. Field of the Invention
The present invention relates to towed low-noise linear acoustic antennas intended especially for subsea seismic exploration. In this field, these antennas are known as  less than  less than streamers greater than  greater than .
2. Discussion of the Background
PCT patent application WO 96/24861 discloses a towed linear antenna (TLA) consisting mainly of a jacket provided with cables made of  less than  less than KEVLAR greater than  greater than  (registered trademark) in order to ensure tensile strength, with rings to ensure radial strength of the jacket and with a cellular open-cell foam filling all of the inside of the jacket. This foam, in which the hydrophones and the electronic circuits are embedded, is impregnated with a dielectric oil having a density of less than 1, making it possible to ensure buoyancy of the antenna (density equal to that of seawater).
The major drawback of this technique is the fact that the vibrations induced by towing are transmitted via the  less than  less than KEVLAR greater than  greater than  cables to the jacket and then to the hydrophones. There is therefore acoustic coupling between the hydrophones and the structure.
A solution which does not have the aforementioned drawbacks is also known from U.S. Pat. No. 4,300,218. That solution isolates each hydrophone in a metal casing, which is itself decoupled from the structure. This technique is known as the xe2x80x9cfree-floodedxe2x80x9d technique. It is also necessary for the spaces between the hydrophones to be filled with a low-density material in order to ensure buoyancy. This solution is expensive, especially with regard to the fill material, and does not allow the diameter to be reduced to the value that would be desired, for example 40 mm.
To alleviate these drawbacks, the invention provides a towed low-noise linear acoustic antenna, comprising a jacket containing a set of hydrophones linked by connections, principally characterized in that the jacket has a set of holes distributed over its surface and allowing the external medium in which the antenna is submerged to be brought into communication with the inside of this antenna, in order to acoustically decouple the hydrophones from the structure of the antenna.
According to another feature, the holes are distributed over the surface of the antenna along a helical line.
According to another feature, the area of all these holes represents about a few cm2 per linear meter.
According to another feature, the jacket is manufactured from a material lightened by hollow inclusions, in order to ensure buoyancy of the antenna.
According to another feature, these inclusions are microspheres.
According to another feature, the material is polyurethane.
According to another feature, the hydrophones are contained in sealed plastic envelopes filled with a substance allowing electrical isolation from the external medium and matching of the acoustic impedance.
According to another feature, the free space inside the jacket is filled with open-cell foam.